Calculus, or tartar as it is sometimes called, is the solid, hard mass of calcified material deposited on and adhering to the surfaces of the teeth. It is composed of inorganic salts which make the calculus hard and resistant to removal. Calculus is largely calcium phosphates, mainly hydroxyapatite with varying, but small, amounts of other inorganic salts.
Although not entirely understood, the general concept is that plaque, which is a sticky film of oral bacteria and their products, adheres to teeth and becomes calcified with the ultimate formation on the teeth of a hard mineral-like material consisting of calcium hydroxyapatite.
As the mature calculus develops, it becomes visibly white or yellowish in color unless stained or discolored by some extraneous agent. In addition to being unsightly and undesirable from an aesthetic standpoint, the mature calculus deposits can be constant sources of irritation to the gingiva. Further, the calculus can promote and retain plaque accumulations. Plaque is recognized as a prime etiological agent involved in gingivitis and periodontal disease. Additionally, plaque is porous and can retain toxic bacterial end products which are also associated with periodontal disease.
Methods for chemically reducing or preventing calculus formation have been directed at affecting the process at any of several stages in its development. One approach is to develop agents which inhibit the formation of the crystalline calcium phosphate or hydroxyapatite.
A wide variety of chemical and biological agents have been suggested to retard calculus formation or to remove calculus after it is formed. The chemical approach to calculus inhibition generally involves crystal growth inhibition which prevents the calculus from forming. Generally, once formed, mechanical removal by the dentist is necessary and is a routine dental office procedure.
The most widely used tartar control agents in dentrifices are sodium and potassium salts of pyrophosphoric acid. It is important that the pyrophosphate salt be in a readily available form so that the pyrophosphate ions (P.sub.2 O.sub.7.sup.-4) contact the enamel surfaces during use. The bioavailability of the ion is determined by the solubility of the salt both in the liquid vehicle of the dentrifice and in the water/expectorant mixture in which the dentrifice is dispersed during brushing of the teeth.
In a dentrifice containing sodium bicarbonate, i.e., baking soda, and the alkali metal salts of pyrophosphoric acid, the solubility of the pyrophosphate salt within the liquid vehicle of the dentrifice is greatly reduced. This suppression of solubility is due to the excess of sodium ions placed in solution by the sodium bicarbonate.
Therefore, there is a need to improve the solubility of alkali metal pyrophosphate salts within a baking soda tooth paste.